Keywords:

Saliva;

immunomodulation;

immunosuppression;

blood-feeding;

ectoparasite

SUMMARY

Saliva of many vector arthropods contains factors that inhibit haemostatic responses in their vertebrate hosts. Less is known about the effect of vector saliva on host immune responses. We investigated the effect of Aedes aegypti salivary gland extracts on antigen-stimulated responses of transgenic OVA-TCR DO11 mouse splenocytes in vitro. T-cell proliferation was inhibited in a dose-dependent manner, with greater than 50% inhibition at 0·3 salivary gland pair (SGP) equivalents/mL. LPS-stimulated B-cell proliferation was also inhibited. Secretion of the Th1 cytokines IL-2 and IFN-γ was reduced by 50% or more with 0·45–0·6 SGP/mL, as was secretion of the pro-inflammatory cytokines GM-CSF and TNF-α, and the Th2 cytokine IL-5. The Th2 cytokines IL-4 and IL-10 were similarly reduced with 0·6–2 SGP/mL. Inhibition of lymphocyte function involved modulation of viable T-cells at low salivary gland extract (SGE) concentrations, and decreased viability at higher concentrations. Dendritic cells were not killed by salivary gland extracts at concentrations as high as 25 salivary gland pairs/mL, but secretion of IL-12 was inhibited by 87% following exposure to 0·6 SGP/mL. Activity is present in saliva and extracts of female but not male salivary glands, and it is depleted from salivary glands of blood-fed mosquitoes. The activity is denatured by boiling and by digestion with the protease papain, indicating a protein; gel filtration HPLC indicates a mass of about 387 kDa. These results suggest that A. aegypti saliva exerts a marked immunomodulatory influence on the environment at the bite site.